In-situ-etch-assisted HDP deposition using SiF4

ABSTRACT

A process is provided for depositing an undoped silicon oxide film on a substrate disposed in a process chamber. A process gas that includes SiF 4 , a fluent gas, a silicon source, and an oxidizing gas reactant is flowed into the process chamber. A plasma having an ion density of at least 10 11  ions/cm 3  is formed from the process gas. The undoped silicon oxide film is deposited over the substrate with the plasma using a process that has simultaneous deposition and sputtering components.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application. Ser. No.10/655,230, entitled “IN-SITU-ETCH-ASSISTED HDP DEPOSITION USING SIF₄,”filed Sep. 3, 2003 now U.S. Pat. No. 6,903,031, by M. Ziaul Karim etal., the entire disclosure of which is incorporated herein by referencefor all purposes.

BACKGROUND OF THE INVENTION

One of the primary steps in the fabrication of modern semiconductordevices is the formation of a thin film on a semiconductor substrate bychemical reaction of gases. Such a deposition process is referred togenerally as chemical vapor deposition (“CVD”). Conventional thermal CVDprocesses supply reactive gases to the substrate surface, whereheat-induced chemical reactions take place to produce a desired film.Plasma-enhanced CVD (“PECVD”) techniques, on the other hand, promoteexcitation and/or dissociation of the reactant gases by the applicationof radio-frequency (“RF”) energy to a reaction zone near the substratesurface, thereby creating a plasma. The high reactivity of the speciesin the plasma reduces the energy required for a chemical reaction totake place, and thus lowers the temperature required for such CVDprocesses as compared with conventional thermal CVD processes. Theseadvantages are further exploited by high-density-plasma (“HDP”) CVDtechniques, in which a dense plasma is formed at low vacuum pressures sothat the plasma species are even more reactive.

Any of these CVD techniques may be used to deposit conductive orinsulative films during the fabrication of integrated circuits. Forapplications such as the deposition of insulating films as premetal orintermetal dielectric layers in an integrated circuit or for shallowtrench isolation, one important physical property of the CVD film is itsability to fill gaps completely between adjacent structures withoutleaving voids; this property is referred to as the film's gapfillcapability. Gaps that may require filling include spaces betweenadjacent raised structures such as transistor gates, conductive lines,etched trenches, or the like.

As semiconductor device geometries have decreased in size over theyears, the ratio of the height of such gaps to their width, theso-called “aspect ratio,” has increased dramatically. Gaps having acombination of high aspect ratio and a small width present a particularchallenge for semiconductor manufacturers to fill completely. In short,the challenge usually is to prevent the deposited film from growing in amanner that closes off the gap before it is filled. Failure to fill thegap completely results in the formation of voids in the deposited layer,which may adversely affect device operation such as by trappingundesirable impurities. The semiconductor industry has accordingly beensearching aggressively for techniques that may improve gapfillcapabilities, particularly with high-aspect-ratio small-width gaps.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention thus provide a process for depositing anundoped silicon oxide film on a substrate that provides good gapfillcharacteristics. The process comprises an in situ etch-assisteddeposition process in which the etchant is provided by SiF₄, togetherwith H₂ to control the deposition to etch ratio, to reduce fluorineconcentration in the deposited film, and to provide other benefits. AnHDP CVD process is used in which the temperature of the substrate isallowed to be sufficiently high to prevent formation of a fluorinatedsilicon oxide layer.

Thus, in embodiments of the invention, a method is provided fordepositing an undoped silicon oxide film on a substrate disposed in aprocess chamber. A process gas comprising SiF₄, H₂, a silicon source,and an oxidizing gas reactant is flowed into the process chamber. Aplasma having an ion density of at least 10¹¹ ions/cm³ is formed fromthe process gas. The undoped silicon oxide film is deposited over thesubstrate with the plasma using a process that has simultaneousdeposition and sputtering components. A temperature of the substrateduring such depositing is greater than 450° C.

In some such embodiments, the temperature of the substrate may besubstantially between 500 and 800° C., while in other such embodiments,the temperature of the substrate may be substantially between 700 and800° C. The silicon source may comprise SiH₄, in which case a ratio of aflow rate of SiF₄ to a flow rate of SiH₄ may be substantially between0.5 and 3.0. The oxidizing gas reactant may comprise O₂. In some suchinstances, the flow rate of H₂ may be less than 1500 sccm. Moregenerally, the flow rate of O₂ may be greater than a factor times a sumof the flow rate of SiF₄ and the flow rate of SiH₄. This factor is lessthan about 1.8 for a flow rate of H₂ to the process chamber less thanabout 300 sccm and is between about 1.8 and 3.0 for a flow rate of H₂ tothe process chamber greater than about 300 sccm. In some embodiments,the process gas may also comprise an inert gas, such as He or Ar.

Deposition of the silicon oxide film may form part of a multidepositionprocess, such as a dep/etch/dep process. In such an instance, theundoped silicon oxide film may be a first portion of an undoped siliconoxide layer, with the method further comprising depositing a secondportion of the undoped silicon oxide layer over the substrate. One ofthe first and second portions of the undoped silicon oxide layer isetched between depositing the undoped silicon oxide film and depositingthe second portion of the undoped silicon oxide layer. In oneembodiment, depositing the second portion of the undoped silicon oxidelayer is performed before the etching and depositing the undoped siliconoxide film is performed after the etching. Depositing the second portionof the undoped silicon oxide layer may be performed similarly todepositing the undoped silicon oxide film, i.e. by flowing a secondprocess gas comprising SiF₄, H₂, the silicon source, and the oxidizinggas reactant, with a second plasma being formed from the second processgas to deposit the second portion at a temperature greater than 450° C.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic cross-sectional drawings illustrating theformation of a void during a gapfill process;

FIGS. 2A and 2B are flow diagrams illustrating methods for depositing anundoped silicon oxide film or layer to fill a gap in embodiments of theinvention;

FIG. 3 provides schematic cross-sectional drawings illustrating how ahigh-aspect-ratio feature may be filled using a dep/etch/dep processaccording to an embodiment of the invention;

FIG. 4A is a simplified diagram of one embodiment of ahigh-density-plasma chemical-vapor deposition system according to thepresent invention;

FIG. 4B is a simplified cross section of a gas ring that may be used inconjunction with the exemplary CVD processing chamber of FIG. 4A;

FIG. 4C is a simplified diagram of a monitor and light pen that may beused in conjunction with the exemplary CVD processing chamber of FIG.4A;

FIG. 4D is a flow chart of an exemplary process control computer programproduct used to control the exemplary CVD processing chamber of FIG. 4A;

FIGS. 5A and 5B present micrograph images from a first experimentillustrating the gapfill capabilities of embodiments of the invention;and

FIGS. 6A and 6B present micrograph images from a second experimentillustrating the gapfill capabilities of embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention pertain to a high-density-plasmachemical-vapor-deposition (“HDP-CVD”) process for depositing undopedsilicon oxide films or layers in shallow trench isolation (“STI”),premetal dielectric (“PMD”), intermetal dielectric (“IMD”), and otherapplications. In the drawings, references to undoped silicon oxide aresometimes made with the acronym “USG,” which refers to “undoped silicateglass.” Embodiments of the invention permit the dielectric material tobe deposited with substantially 100% gapfill for integrated circuitshaving minimum feature sizes of 0.10 μm or less; bottom-up gapfill maybe achieved inside very aggressive trenches having aspect ratios greaterthan 5.5:1. As used herein, the terms “film” and “layer” are intended torefer interchangeably to a thickness of material, although in describingembodiments in which material is deposited with interleaved depositionand etching steps, the completed structure is sometimes referred to as alayer, with the material deposited in each deposition step referred toas a film comprised by that layer. Processes that include interleaveddeposition and etching steps are sometimes referred to as“deposition/etch/deposition” or “dep/etch/dep” processes.

The gapfill problem addressed by embodiments of the invention isillustrated schematically with the cross-sectional views shown in FIGS.1A and 1B. FIG. 1A shows a vertical cross section of a substrate 110,such as may be provided with a semiconductor wafer, having a layer offeatures 120. Adjacent features define gaps 114 that are to be filledwith dielectric material 118, with the sidewalls 116 of the gaps beingdefined by the surfaces of the features 120. As the deposition proceeds,dielectric material 118 accumulates on the surfaces of the features 120,as well as on the substrate 110 and forms overhangs 122 at the corners124 of the features 120. As deposition of the dielectric material 118continues, the overhangs 122 typically grow faster than the gap 114 in acharacteristic breadloafing fashion. Eventually, the overhangs 122 growtogether to form the dielectric layer 126 shown in FIG. 1B, preventingdeposition into an interior void 128.

CVD deposition of undoped silicon oxide films typically proceeds byflowing a process gas into a process chamber with the process gascomprising a silicon source and an oxidizing gas reactant. The siliconsource typically comprises a silane such as SiH₄ and the oxidizing gasreactant typically comprises O₂. Sometimes an inert gas such as Ar mayalso be included as a fluent gas. Improved gapfill characteristics havegenerally been achieved using HDP-CVD because the high density of ionicspecies in the plasma during an HDP-CVD process causes there to besputtering of a film even while it is being deposited. This combinationof simultaneous sputtering and deposition tends to keep the gap openduring deposition, although there remain limits to gapfill capabilitywith such processes.

The inventors have discovered that the effects of including SiF₄ andincluding H₂ during the deposition combine synergistically to improvegapfill capability of HDP-CVD deposition of undoped silicon oxide. Thesupply of fluorine ions in the plasma by including SiF₄ acts as an insitu etchant to complement the natural sputtering of the HDP-CVDprocess, but minimizes aggressive components of the etching. Suchaggressive components, which are produced when nitrofluorinated etchinggases such as NF₃ or carbofluorinated etching gases such as C₂F₆, C₃F₈,or CF₄, are used as in situ etchants are undesirable because they maycause corner clipping of structural features defining the gap beingfilled. Such corner clipping occurs when the aggressive etch acts atregions of the gap profile where deposition components are relativelylow, e.g. at the top corners of the gap profile, and may causesignificant damage to structural features that define the gap. In someinstances, such structural features may include a thin SiN or SiC linerthat may be used in some processes to line a gap or trench. The use ofSiF₄ reduces such aggressive etch components and reduces the possibilityof corner clipping even while providing good bottom-up gapfillcapabilities for appropriate relative flow rates of the SiF₄ and siliconsource as described below.

The use of H₂ also acts to reduce the possibility of corner clipping bycontrolling the relative deposition-to-etch ratio of the process gas. Inparticular, the H₂ also reduces the concentration of fluorine atoms inthe plasma to control aggressive etch components and also acts to reducethe incorporation of fluorine into the deposited film. In addition, theH₂ acts to reduce redeposition of fluorine-rich material and eliminatesthe accumulation of excess fluorine at redeposition sites that istypical of in situ etch-assisted (“ISEA”) processes. It also reduces thepossibility of metal contamination in the film that may result frometching of material from the process chamber, such as Al contamination.

The resulting process is summarized for one embodiment with the flowdiagram shown in FIG. 2A. At block 204, the process gas comprising SiF₄,H₂, the silicon source, and the oxidizing gas reactant are flowed intothe process chamber. Suitable flow rates for the different precursorgases may vary depending on specific applications and on the design ofthe chamber in which the deposition is performed. In an embodiment inwhich the silicon source comprises SiH₄ and the oxidizing gas reactantcomprises O₂, suitable flow rates

are as follows: for SiH₄, the flow rate

(SiH₄) for the chamber design described below may be between about 15and 100 sccm; for O₂, the flow rate

(O₂) may be between about 25 and 500 sccm; for SiF₄, the flow rate

(SiF₄) may be between about 15 and 100 sccm; and for H₂, the flow rate

(H₂) may be between about 50 and 1000 sccm.

While these ranges set forth broad parameters for the flow rates, it isgenerally desirable for the flow rates for each of the precursor gasesnot to be set independently, but to be determined relative to eachother. For example, in one set of embodiments, the flow rate for SiF₄divided by the flow rate for SiH₄,

(SiF₄)/

(SiH₄) is between about 0.5 and 3.0. In one such embodiment, the flowrates for SiF₄ and for SiH₄ are substantially equal. The flow rate forO₂ may be related both to the flow rate of H₂ and to the combined flowrate of SiF₄ and SiH₄ as follows:

(O ₂)=α[

(H ₂)][

(SiF ₄)+

(SiH ₄)],where the factor α varies depending on the flow rate of H₂. When theflow rate of H₂ is low, i.e. less than about 300 sccm, the factor α maybe less than about 1.8, but when the flow rate of H₂ is high, i.e.greater than about 300 sccm, the factor α may be between 1.8 and 3.0.The variation in the factor α reflects the fact that higher O₂ flowrates are appropriate relative to the total SiF₄ and SiH₄ flow rateswhen the H₂ flow rate is increased.

In some embodiments, an inert gas may also be supplied as a component ofthe process gas, such as a flow of He, Ne, or Ar. The level ofsputtering provided by the H₂ or the inert gas is inversely related totheir molecular or atomic mass, with H₂ being used because it provideseven less sputtering that He. Inclusion of an inert gas with the H₂ may,however, provides better deposition uniformity than use of H₂ alone andmay permit a significant cost saving. These benefits are realized evenwhere the amount of H₂ used in the premixture is significantly greaterthan the amount of the inert gas. For example, in one embodiment, thepremixture comprises greater than 95 wt. % H₂ and in another embodimentcomprises greater than 99 wt. % H₂.

At block 208, a high-density plasma is formed in the process chamberfrom the process gas. The ion density of such a high-density plasma isgenerally greater than 10¹¹ ions/cm³. In embodiments of the invention,the substrate temperature is allowed to reach a relatively hightemperature, i.e. greater than 450° C. as indicated at block 216. Such ahigh temperature may be provided by the plasma with relatively little,if any, cooling of the substrate. In some embodiments, the temperatureof the substrate is allowed to remain substantially between 500 and 800°C. or substantially between 700 and 800° C. during deposition. Such ahigh temperature results in relatively little fluorine beingincorporated into the film when the film is deposited with the plasmausing the HDP-CVD process as indicated at block 216. The fluorineconcentration in the resulting film is generally less than 1.0 at. % andmay be as low as 0.008 at. %. In this way, an undoped silicon oxide filmmay be deposited, even though the chemistry of the reaction is similarto a chemistry that may be used in other HDP-CVD processes to depositfluorinated silicon oxide. Such fluorinated silicon oxide films areusually formed with a substrate temperature of about 350° C., typicallyhave a much higher fluorine concentration in the range of 4–8 at. %, anddo not enjoy the benefits of improved bottom-up gapfill provided by thecombination of limitations disclosed herein. It should thus berecognized that as used herein, an “undoped silicon oxide film” maycomprise some impurities in addition to the silicon and oxygen that makeup the film, but that the concentration of such impurities is small. Inparticular, the fluorine concentration is less than 1.0 at. %.

The specific order of the blocks shown in FIG. 2A is not intended to berestrictive and in other embodiments, the corresponding steps may beperformed in an alternative order. For example, allowing the temperatureto reach a temperature greater than 450° C. as indicated at block 216may be performed prior to flowing the gas reactants into the processchamber at block 204 and/or prior to forming the high-density plasma asindicated at block 208. Furthermore, the inclusion of specific blocks inFIG. 2A is not intended to be restrictive since additional steps may beperformed in alternative embodiments.

In some embodiments of the invention, the film deposition described inconnection with FIG. 2A may correspond to one deposition step in adep/etch/dep process. Such a dep/etch/dep process is illustrated withthe flow diagram of FIG. 2B, in which deposition of first and secondportions of the undoped silicon oxide as indicated at blocks 240 and 248are separated by an intermediate etching of the first portion at block244. Such etching may be performed in situ or remotely. In someinstances, the etching may be also be preceded by a cooling step tolower the temperature of the substrate below about 250° C. and therebyprovide better etch control. Such cooling may be performed, for example,by helium backside cooling of the substrate, among other methods. Incertain in situ embodiments, a nitrofluorinated gas such as NF₃ or acarbofluorinated gas such as C₂F₆, C₃F₈, or CF₄, is flowed into theprocess chamber. Approximately 5–15% of the deposited thickness of thesilicon oxide film may be removed during the etching step, although theamount removed may vary at different points according to the profile ofthe film. At least one of the deposition steps is performed with thedeposition method described in connection with FIG. 2A. In a specificembodiment, that deposition method is used for the second of thedeposition steps 248 shown in FIG. 2B. The dashed arrow in FIG. 2B isintended to indicate that the interleaving of depositing and etchingsteps may continue indefinitely, with more interleaved steps being usedfor more aggressive gapfill applications.

In embodiments of the invention that use a dep/etch/dep process, care istaken not to damage the underlying structures during the etching step244. This may be accomplished with a combination of effects that includeensuring that sufficient material is deposited during the firstdeposition step 240 to protect the underlying structures and that theetching conditions during the etching step 244 do not etch away so muchmaterial that the structures are exposed. The patterns that result fromprocess parameters that are used to achieve this combination of effectsare illustrated schematically in FIG. 3.

The initial substrate structure 301 is shown schematically as includingfeatures 300 that are to be filled with a dielectric material. Theprocess conditions for the first deposition may result in the formationof a significant cusp 308, as shown for intermediate structure 302, withdielectric material being deposited more thickly near the corners of theunderlying structures than on the sidewalls. Structure 302 may resultfrom deposition of a first film using the method described in connectionwith FIG. 2A. The cusp feature is protective during the subsequentetching step, which results in structure 303. Performing the etchanisotropically, such as by applying a bias during a reactive etch,helps to shape the deposited layer 310 so that the basic shape of theoriginal features 300 are retained, but are less severe, with thecorners of the underlying structures remaining unexposed. When the finaldeposition is performed, the features 300 may then be filled completelywith dielectric material 312, such as shown schematically with structure304.

The methods described above may be implemented with a variety of HDP-CVDsystems, some of which are described in detail in connection with FIGS.4A–4D. FIG. 4A schematically illustrates the structure of such anHDP-CVD system 410 in one embodiment. The system 410 includes a chamber413, a vacuum system 470, a source plasma system 480A, a bias plasmasystem 480B, a gas delivery system 433, and a remote plasma cleaningsystem 450.

The upper portion of chamber 413 includes a dome 414, which is made of aceramic dielectric material, such as aluminum oxide or aluminum nitride.Dome 414 defines an upper boundary of a plasma processing region 416.Plasma processing region 416 is bounded on the bottom by the uppersurface of a substrate 417 and a substrate support member 418.

A heater plate 423 and a cold plate 424 surmount, and are thermallycoupled to, dome 414. Heater plate 423 and cold plate 424 allow controlof the dome temperature to within about ±10° C. over a range of about100° C. to 200° C. This allows optimizing the dome temperature for thevarious processes. For example, it may be desirable to maintain the domeat a higher temperature for cleaning or etching processes than fordeposition processes. Accurate control of the dome temperature alsoreduces the flake or particle counts in the chamber and improvesadhesion between the deposited layer and the substrate.

The lower portion of chamber 413 includes a body member 422, which joinsthe chamber to the vacuum system. A base portion 421 of substratesupport member 418 is mounted on, and forms a continuous inner surfacewith, body member 422. Substrates are transferred into and out ofchamber 413 by a robot blade (not shown) through an insertion/removalopening (not shown) in the side of chamber 413. Lift pins (not shown)are raised and then lowered under the control of a motor (also notshown) to move the substrate from the robot blade at an upper loadingposition 457 to a lower processing position 456 in which the substrateis placed on a substrate receiving portion 419 of substrate supportmember 418. Substrate receiving portion 419 includes an electrostaticchuck 420 that secures the substrate to substrate support member 418during substrate processing. In a preferred embodiment, substratesupport member 418 is made from an aluminum oxide or aluminum ceramicmaterial.

Vacuum system 470 includes throttle body 425, which houses twin-bladethrottle valve 426 and is attached to gate valve 427 and turbo-molecularpump 428. It should be noted that throttle body 625 offers minimumobstruction to gas flow, and lows symmetric pumping. Gate valve 427 canisolate pump 428 from throttle body 425, and can also control chamberpressure by restricting the exhaust flow capacity when throttle valve426 is fully open. The arrangement of the throttle valve, gate valve,and turbo-molecular pump allow accurate and stable control of chamberpressures from between about 1 millitorr to about 2 torr.

The source plasma system 480A includes a top coil 429 and side coil 430,mounted on dome 414. A symmetrical ground shield (not shown) reduceselectrical coupling between the coils. Top coil 429 is powered by topsource RF (SRF) generator 431A, whereas side coil 430 is powered by sideSRF generator 431B, allowing independent power levels and frequencies ofoperation for each coil. This dual coil system allows control of theradial ion density in chamber 413, thereby improving plasma uniformity.Side coil 430 and top coil 429 are typically inductively driven, whichdoes not require a complimentary electrode. In a specific embodiment,the top source RF generator 431A provides up to 2,500 watts of RF powerat nominally 2 MHz and the side source RF generator 431B provides up to5,000 watts of RF power at nominally 2 MHz. The operating frequencies ofthe top and side RF generators may be offset from the nominal operatingfrequency (e.g. to 1.7–1.9 MHz and 1.9–2.1 MHz, respectively) to improveplasma-generation efficiency.

A bias plasma system 480B includes a bias RF (“BRF”) generator 431C anda bias matching network 432C. The bias plasma system 480B capacitivelycouples substrate portion 417 to body member 422, which act ascomplimentary electrodes. The bias plasma system 480B serves to enhancethe transport of plasma species (e.g., ions) created by the sourceplasma system 480A to the surface of the substrate. In a specificembodiment, bias RF generator provides up to 5,000 watts of RF power at13.56 MHz.

RF generators 431A and 431B include digitally controlled synthesizersand operate over a frequency range between about 1.8 to about 2.1 MHz.Each generator includes an RF control circuit (not shown) that measuresreflected power from the chamber and coil back to the generator andadjusts the frequency of operation to obtain the lowest reflected power,as understood by a person of ordinary skill in the art. RF generatorsare typically designed to operate into a load with a characteristicimpedance of 50 ohms. RF power may be reflected from loads that have adifferent characteristic impedance than the generator. This can reducepower transferred to the load. Additionally, power reflected from theload back to the generator may overload and damage the generator.Because the impedance of a plasma may range from less than 5 ohms toover 900 ohms, depending on the plasma ion density, among other factors,and because reflected power may be a function of frequency, adjustingthe generator frequency according to the reflected power increases thepower transferred from the RF generator to the plasma and protects thegenerator. Another way to reduce reflected power and improve efficiencyis with a matching network.

Matching networks 432A and 432B match the output impedance of generators431A and 431B with their respective coils 429 and 430. The RF controlcircuit may tune both matching networks by changing the value ofcapacitors within the matching networks to match the generator to theload as the load changes. The RF control circuit may tune a matchingnetwork when the power reflected from the load back to the generatorexceeds a certain limit. One way to provide a constant match, andeffectively disable the RF control circuit from tuning the matchingnetwork, is to set the reflected power limit above any expected value ofreflected power. This may help stabilize a plasma under some conditionsby holding the matching network constant at its most recent condition.

Other measures may also help stabilize a plasma. For example, the RFcontrol circuit can be used to determine the power delivered to the load(plasma) and may increase or decrease the generator output power to keepthe delivered power substantially constant during deposition of a layer.

A gas delivery system 433 provides gases from several sources, 434A–434Echamber for processing the substrate via gas delivery lines 438 (onlysome of which are shown). As would be understood by a person of skill inthe art, the actual sources used for sources 434A–434E and the actualconnection of delivery lines 438 to chamber 413 varies depending on thedeposition and cleaning processes executed within chamber 413. Gases areintroduced into chamber 413 through a gas ring 437 and/or a top nozzle445. FIG. 4B is a simplified, partial cross-sectional view of chamber413 showing additional details of gas ring 437.

In one embodiment, first and second gas sources, 434A and 434B, andfirst and second gas flow controllers, 435A′ and 435B′, provide gas toring plenum 436 in gas ring 437 via gas delivery lines 438 (only some ofwhich are shown). Gas ring 437 has a plurality of source gas nozzles 439(only one of which is shown for purposes of illustration) that provide auniform flow of gas over the substrate. Nozzle length and nozzle anglemay be changed to allow tailoring of the uniformity profile and gasutilization efficiency for a particular process within an individualchamber. In a preferred embodiment, gas ring 437 has 12 source gasnozzles made from an aluminum oxide ceramic.

Gas ring 437 also has a plurality of oxidizer gas nozzles 440 (only oneof which is shown), which in a preferred embodiment are co-planar withand shorter than source gas nozzles 439, and in one embodiment receivegas from body plenum 441. In some embodiments it is desirable not to mixsource gases and oxidizer gases before injecting the gases into chamber413. In other embodiments, oxidizer gas and source gas may be mixedprior to injecting the gases into chamber 413 by providing apertures(not shown) between body plenum 441 and gas ring plenum 436. In oneembodiment, third, fourth, and fifth gas sources, 434C, 434D, and 434D′,and third and fourth gas flow controllers, 435C and 435D′, provide gasto body plenum via gas delivery lines 438. Additional valves, such as443B (other valves not shown), may shut off gas from the flowcontrollers to the chamber.

In embodiments where flammable, toxic, or corrosive gases are used, itmay be desirable to eliminate gas remaining in the gas delivery linesafter a deposition. This may be accomplished using a 3-way valve, suchas valve 443B, to isolate chamber 413 from delivery line 438A and tovent delivery line 438A to vacuum foreline 444, for example. As shown inFIG. 4A, other similar valves, such as 443A and 443C, may beincorporated on other gas delivery lines. Such three-way valves may beplaced as close to chamber 413 as practical, to minimize the volume ofthe unvented gas delivery line (between the three-way valve and thechamber). Additionally, two-way (on-off) valves (not shown) may beplaced between a mass flow controller (“MFC”) and the chamber or betweena gas source and an MFC.

Referring again to FIG. 4A, chamber 413 also has top nozzle 445 and topvent 446. Top nozzle 445 and top vent 446 allow independent control oftop and side flows of the gases, which improves film uniformity andallows fine adjustment of the film's deposition and doping parameters.Top vent 446 is an annular opening around top nozzle 445. In oneembodiment, first gas source 434A supplies source gas nozzles 439 andtop nozzle 445. Source nozzle MFC 435A′ controls the amount of gasdelivered to source gas nozzles 439 and top nozzle MFC 435A controls theamount of gas delivered to top gas nozzle 445. Similarly, two MFCs 435Band 435B′ may be used to control the flow of oxygen to both top vent 446and oxidizer gas nozzles 440 from a single source of oxygen, such assource 434B. The gases supplied to top nozzle 445 and top vent 446 maybe kept separate prior to flowing the gases into chamber 413, or thegases may be mixed in top plenum 448 before they flow into chamber 413.Separate sources of the same gas may be used to supply various portionsof the chamber.

A remote microwave-generated plasma cleaning system 450 is provided toperiodically clean deposition residues from chamber components. Thecleaning system includes a remote microwave generator 451 that creates aplasma from a cleaning gas source 434E (e.g., molecular fluorine,nitrogen trifluoride, other fluorocarbons or equivalents) in reactorcavity 453. The reactive species resulting from this plasma are conveyedto chamber 413 through cleaning gas feed port 454 via applicator tube455. The materials used to contain the cleaning plasma (e.g., cavity 453and applicator tube 455) must be resistant to attack by the plasma. Thedistance between reactor cavity 453 and feed port 454 should be kept asshort as practical, since the concentration of desirable plasma speciesmay decline with distance from reactor cavity 453. Generating thecleaning plasma in a remote cavity allows the use of an efficientmicrowave generator and does not subject chamber components to thetemperature, radiation, or bombardment of the glow discharge that may bepresent in a plasma formed in situ. Consequently, relatively sensitivecomponents, such as electrostatic chuck 420, do not need to be coveredwith a dummy wafer or otherwise protected, as may be required with an insitu plasma cleaning process. In one embodiment, this cleaning system isused to dissociate atoms of the etchant gas remotely, which are thensupplied to the process chamber 413. In another embodiment, the etchantgas is provided directly to the process chamber 413. In still a furtherembodiment, multiple process chambers are used, with deposition andetching steps being performed in separate chambers.

System controller 460 controls the operation of system 410. In apreferred embodiment, controller 460 includes a memory 462, such as ahard disk drive, a floppy disk drive (not shown), and a card rack (notshown) coupled to a processor 461. The card rack may contain asingle-board computer (SBC) (not shown), analog and digital input/outputboards (not shown), interface boards (not shown), and stepper motorcontroller boards (not shown). The system controller conforms to theVersa Modular European (“VME”) standard, which defines board, card cage,and connector dimensions and types. The VME standard also defines thebus structure as having a 16-bit data bus and 24-bit address bus. Systemcontroller 431 operates under the control of a computer program storedon the hard disk drive or through other computer programs, such asprograms stored on a removable disk. The computer program dictates, forexample, the timing, mixture of gases, RF power levels and otherparameters of a particular process. The interface between a user and thesystem controller is via a monitor, such as a cathode ray tube (“CRT”)465, and a light pen 466, as depicted in FIG. 4C.

FIG. 4C is an illustration of a portion of an exemplary system userinterface used in conjunction with the exemplary CVD processing chamberof FIG. 4A. System controller 460 includes a processor 461 coupled to acomputer-readable memory 462. Preferably, memory 462 may be a hard diskdrive, but memory 462 may be other kinds of memory, such as ROM, PROM,and others.

System controller 460 operates under the control of a computer program463 stored in a computer-readable format within memory 462. The computerprogram dictates the timing, temperatures, gas flows, RF power levelsand other parameters of a particular process. The interface between auser and the system controller is via a CRT monitor 465 and a light pen466, as depicted in FIG. 4C. In a preferred embodiment, two monitors,465 and 465A, and two light pens, 466 and 466A, are used, one mounted inthe clean room wall (665) for the operators and the other behind thewall (665A) for the service technicians. Both monitors simultaneouslydisplay the same information, but only one light pen (e.g. 466) isenabled. To select a particular screen or function, the operator touchesan area of the display screen and pushes a button (not shown) on thepen. The touched area confirms being selected by the light pen bychanging its color or displaying a new menu, for example.

The computer program code can be written in any conventionalcomputer-readable programming language such as 68000 assembly language,C, C++, or Pascal. Suitable program code is entered into a single file,or multiple files, using a conventional text editor and is stored orembodied in a computer-usable medium, such as a memory system of thecomputer. If the entered code text is in a high level language, the codeis compiled, and the resultant compiler code is then linked with anobject code of precompiled windows library routines. To execute thelinked compiled object code, the system user invokes the object codecausing the computer system to load the code in memory. The CPU readsthe code from memory and executes the code to perform the tasksidentified in the program.

FIG. 4D shows an illustrative block diagram of the hierarchical controlstructure of computer program 500. A user enters a process set numberand process chamber number into a process selector subroutine 510 inresponse to menus or screens displayed on the CRT monitor by using thelight pen interface. The process sets are predetermined sets of processparameters necessary to carry out specified processes, and areidentified by predefined set numbers. Process selector subroutine 510identifies (i) the desired process chamber in a multichamber system, and(ii) the desired set of process parameters needed to operate the processchamber for performing the desired process. The process parameters forperforming a specific process relate to conditions such as process gascomposition and flow rates, temperature, pressure, plasma conditionssuch as RF power levels, and chamber dome temperature, and are providedto the user in the form of a recipe. The parameters specified by therecipe are entered utilizing the light pen/CRT monitor interface.

The signals for monitoring the process are provided by the analog anddigital input boards of system controller 460, and the signals forcontrolling the process are output on the analog and digital outputboards of system controller 460.

A process sequencer subroutine 520 comprises program code for acceptingthe identified process chamber and set of process parameters from theprocess selector subroutine 510 and for controlling operation of thevarious process chambers. Multiple users can enter process set numbersand process chamber numbers, or a single user can enter multiple processset numbers and process chamber numbers; sequencer subroutine 520schedules the selected processes in the desired sequence. Preferably,sequencer subroutine 520 includes a program code to perform the steps of(i) monitoring the operation of the process chambers to determine if thechambers are being used, (ii) determining what processes are beingcarried out in the chambers being used, and (iii) executing the desiredprocess based on availability of a process chamber and type of processto be carried out. Conventional methods of monitoring the processchambers can be used, such as polling. When scheduling which process isto be executed, sequencer subroutine 520 can be designed to take intoconsideration the “age” of each particular user-entered request, or thepresent condition of the process chamber being used in comparison withthe desired process conditions for a selected process, or any otherrelevant factor a system programmer desires to include for determiningscheduling priorities.

After sequencer subroutine 520 determines which process chamber andprocess set combination is going to be executed next, sequencersubroutine 520 initiates execution of the process set by passing theparticular process set parameters to a chamber manager subroutine530A–530C, which controls multiple processing tasks in chamber 413 andpossibly other chambers (not shown) according to the process set sent bysequencer subroutine 520.

Examples of chamber component subroutines are substrate positioningsubroutine 540, process gas control subroutine 550, pressure controlsubroutine 560, and plasma control subroutine 570. Those having ordinaryskill in the art will recognize that other chamber control subroutinescan be included depending on what processes are selected to be performedin chamber 413. In operation, chamber manager subroutine 530Aselectively schedules or calls the process component subroutines inaccordance with the particular process set being executed. Chambermanager subroutine 530A schedules process component subroutines in thesame manner that sequencer subroutine 520 schedules the process chamberand process set to execute. Typically, chamber manager subroutine 530Aincludes steps of monitoring the various chamber components, determiningwhich components need to be operated based on the process parameters forthe process set to be executed, and causing execution of a chambercomponent subroutine responsive to the monitoring and determining steps.

Operation of particular chamber component subroutines will now bedescribed with reference to FIGS. 4A and 4D. Substrate positioningsubroutine 540 comprises program code for controlling chamber componentsthat are used to load a substrate onto substrate support number 418.Substrate positioning subroutine 540 may also control transfer of asubstrate into chamber 413 from, e.g., a plasma-enhanced CVD (“PECVD”)reactor or other reactor in the multi-chamber system, after otherprocessing has been completed.

Process gas control subroutine 550 has program code for controllingprocess gas composition and flow rates. Subroutine 550 controls theopen/close position of the safety shut-off valves and also rampsup/ramps down the mass flow controllers to obtain the desired gas flowrates. All chamber component subroutines, including process gas controlsubroutine 550, are invoked by chamber manager subroutine 530A.Subroutine 550 receives process parameters from chamber managersubroutine 530A related to the desired gas flow rates.

Typically, process gas control subroutine 550 opens the gas supplylines, and repeatedly (i) reads the necessary mass flow controllers,(ii) compares the readings to the desired flow rates received fromchamber manager subroutine 530A, and (iii) adjusts the flow rates of thegas supply lines as necessary. Furthermore, process gas controlsubroutine 550 may include steps for monitoring the gas flow rates forunsafe rates and for activating the safety shut-off valves when anunsafe condition is detected.

In some processes, an inert gas, such as argon, is flowed into chamber413 to stabilize the pressure in the chamber before reactive processgases are introduced. For these processes, the process gas controlsubroutine 550 is programmed to include steps for flowing the inert gasinto chamber 413 for an amount of time necessary to stabilize thepressure in the chamber. The steps described above may then be carriedout.

Additionally, when a process gas is to be vaporized from a liquidprecursor, for example, tetraethylorthosilane (TEOS), the process gascontrol subroutine 550 may include steps for bubbling a delivery gassuch as helium through the liquid precursor in a bubbler assembly or forintroducing the helium to a liquid injection valve. For this type ofprocess, the process gas control subroutine 550 regulates the flow ofthe delivery gas, the pressure in the bubbler, and the bubblertemperature to obtain the desired process gas flow rates. As discussedabove, the desired process gas flow rates are transferred to process gascontrol subroutine 550 as process parameters.

Furthermore, the process gas control subroutine 550 includes steps forobtaining the necessary delivery gas flow rate, bubbler pressure, andbubbler temperature for the desired process gas flow rate by accessing astored table containing the necessary values for a given process gasflow rate. Once the necessary values are obtained, the delivery gas flowrate, bubbler pressure and bubbler temperature are monitored, comparedto the necessary values and adjusted accordingly.

The process gas control subroutine 550 may also control the flow ofheat-transfer gas, such as helium (He), through the inner and outerpassages in the wafer chuck with an independent helium control (IHC)subroutine (not shown). The gas flow thermally couples the substrate tothe chuck. In a typical process, the wafer is heated by the plasma andthe chemical reactions that form the layer, and the He cools thesubstrate through the chuck, which may be water-cooled. This keeps thesubstrate below a temperature that may damage preexisting features onthe substrate.

Pressure control subroutine 460 includes program code for controllingthe pressure in chamber 413 by regulating the size of the opening ofthrottle valve 426 in the exhaust portion of the chamber. There are atleast two basic methods of controlling the chamber with the throttlevalve. The first method relies on characterizing the chamber pressure asit relates to, among other things, the total process gas flow, the sizeof the process chamber, and the pumping capacity. The first method setsthrottle valve 426 to a fixed position. Setting throttle valve 426 to afixed position may eventually result in a steady-state pressure.

Alternatively, the chamber pressure may be measured, with a manometerfor example, and the position of throttle valve 426 may be adjustedaccording to pressure control subroutine 560, assuming the control pointis within the boundaries set by gas flows and exhaust capacity. Theformer method may result in quicker chamber pressure changes, as themeasurements, comparisons, and calculations associated with the lattermethod are not invoked. The former method may be desirable where precisecontrol of the chamber pressure is not required, whereas the lattermethod may be desirable where an accurate, repeatable, and stablepressure is desired, such as during the deposition of a layer.

When pressure control subroutine 560 is invoked, the desired, or target,pressure level is received as a parameter from chamber managersubroutine 530A. Pressure control subroutine 560 measures the pressurein chamber 413 by reading one or more conventional pressure manometersconnected to the chamber; compares the measured value(s) to the targetpressure; obtains proportional, integral, and differential (PID) valuesfrom a stored pressure table corresponding to the target pressure, andadjusts throttle valve 426 according to the PID values obtained from thepressure table. Alternatively, pressure control subroutine 560 may openor close throttle valve 426 to a particular opening size to regulate thepressure in chamber 413 to a desired pressure or pressure range.

Plasma control subroutine 570 comprises program code for controlling thefrequency and power output setting of RF generators 431A and 431B andfor tuning matching networks 432A and 432B. Plasma control subroutine570, like the previously described chamber component subroutines, isinvoked by chamber manager subroutine 530A.

An example of a system that may incorporate some or all of thesubsystems and routines described above would be the ULTIMA™ system,manufactured by APPLIED MATERIALS, INC., of Santa Clara, Calif.,configured to practice the present invention. Further details of such asystem are disclosed in commonly assigned U.S. Pat. No. 6,170,428, filedJul. 15, 1996, entitled “Symmetric Tunable Inductively-Coupled HDP-CVDReactor,” having Fred C. Redeker, Farhad Moghadam, Hirogi Hanawa,Tetsuya Ishikawa, Dan Maydan, Shijian Li, Brian Lue, Robert Steger,Yaxin Wang, Manus Wong and Ashok Sinha listed as co-inventors, thedisclosure of which is incorporated herein by reference. The describedsystem is for exemplary purpose only. It would be a matter of routineskill for a person of skill in the art to select an appropriateconventional substrate processing system and computer control system toimplement the present invention.

EXAMPLE 1

To illustrate the gapfill capability provided with embodiments of theinvention, experiments were performed with a substrate having a trenchbetween adjacent raised surfaces to define a gap having an aspect ratiogreater than 5.0:1. The following flow rates for a process in which theprocess gas during deposition comprised SiH₄, O₂, SiF₄, and H₂ provideda deposition rate of approximately 4700 Å/minute with a substratetemperature between 500 and 800° C.:

Flow Rate Parameter (sccm)

(SiH₄) 33.5

(SiF₄) 37.0 z,214 (H₂) 65

(O₂) 160 z,216 (SiF₄)/

(SiH₄) 1.10 α =

(O₂)/[

(SiF₄) +

(SiH₄)] 2.3As noted in the table, the flow rates for this example fall within theparameter ranges discussed above. Micrographs provided in FIGS. 5A and5B show that substantially 100% gapfill is achieved for the5.0:1-aspect-ratio gap. For purposes of comparison, FIG. 5A provides amicrograph for a process using SiH₄, NF₃, and O₂ for the process gas, inwhich the gap was not adequately filled. The micrograph in FIG. 5B showsthe results using the SiH₄, SiF₄, O₂, and H₂ process gas defined by thetable, in which the gapfill capability is good. The fluorineconcentration in the film produced with the process using the tableparameters was less than 1.0 at. %. The methods of the invention maythus be used in a variety of undoped silicon oxide gapfill applications,including shallow-trench-isolation and premetal-dielectric gapfillapplications.

EXAMPLE 2

To further illustrate the gapfill capability provided with embodimentsof the invention, additional experiments were performed with a substratehaving a trench between adjacent raised surfaces to define a gap alsohaving an aspect ratio greater than 5.0:1. The following flow rates fora process in which the process gas during deposition comprised SiH₄, O₂,SiF₄, and H₂ provided a deposition rate of approximately 2600 Å/minutewith a substrate temperature between 500 and 800° C.:

Flow Rate Parameter (sccm)

(SiH₄) 13.0

(SiF₄) 20.0

(H₂) 620

(O₂) 85

(SiF₄)/

(SiH₄) 1.54 α =

(O₂)/[

(SiF₄) +

(SiH₄)] 2.57As noted in the table, the flow rates for this example also fall withinthe parameter ranges discussed above. Micrographs provided in FIGS. 6Aand 6B show that substantially 100% gapfill is achieved for the5.0:1-aspect-ratio gap. The micrographs in FIGS. 6A and 6B show resultsusing the SiH₄, SiF₄, O₂, and H₂ process gas defined by the table, inwhich the gapfill capability is good with no corner clipping. Thefluorine concentration in the film produced with the process using thetable parameters was less than 1.0 at. %. The methods of the inventionmay thus be used in a variety of undoped silicon oxide gapfillapplications, including shallow-trench-isolation and premetal-dielectricgapfill applications.

Those of ordinary skill in the art will realize that processingparameters can vary for different processing chambers and differentprocessing conditions, and that different precursors can be used withoutdeparting from the spirit of the invention. Other variations will alsobe apparent to persons of skill in the art. These equivalents andalternatives are intended to be included within the scope of the presentinvention. Therefore, the scope of this invention should not be limitedto the embodiments described, but should instead be defined by thefollowing claims.

1. A method for depositing an undoped silicon oxide film on a substratedisposed in a process chamber, the method comprising: flowing a processgas comprising SiF₄, a fluent gas, a silicon source, and an oxidizinggas reactant into the process chamber; forming a plasma having an iondensity of at least 10¹¹ ions/cm³ from the process gas; and depositingthe undoped silicon oxide film over the substrate with the plasma usinga process that has simultaneous deposition and sputtering components,wherein a flow rate of SiF₄ to the process chamber to a flow rate of thesilicon source to the process chamber is substantially between 0.5 and3.0.
 2. The method recited in claim 1 wherein a temperature of thesubstrate during such depositing is substantially between 500 and 800°C.
 3. The method recited in claim 1 wherein a temperature of thesubstrate during such depositing is substantially between 700 and 800°C.
 4. The method recited in claim 1 wherein the silicon source comprisesSiH₄.
 5. The method recited in claim 4 wherein the oxidizing gasreactant comprises O₂.
 6. The method recited in claim 5 wherein thefluent gas comprises H₂ and has a flow rate to the process chamber lessthan 1500 sccm.
 7. The method recited in claim 5 wherein a flow rate ofO₂ to the process chamber is greater than a factor times a sum of theflow rate of SiF₄ and the flow rate of SiH₄ to the process chamber, thefactor being less than about 1.8 for a flow rate of the fluent gas tothe process chamber less than about 300 sccm and being between about 1.8and 3.0 for a flow rate of the fluent gas to the process chamber greaterthan about 300 sccm.
 8. The method recited in claim 1 wherein the fluentgas comprises an inert gas.
 9. The method recited in claim 8 wherein theinert gas comprises He.
 10. The method recited in claim 1 wherein theundoped silicon oxide film is a first portion of an undoped siliconoxide layer, the method further comprising: depositing a second portionof the undoped silicon oxide layer over the substrate; and etching oneof the first and second portions of the undoped silicon oxide layerbetween depositing the undoped silicon oxide film and depositing thesecond portion of the undoped silicon oxide layer.
 11. The methodrecited in claim 10 wherein depositing the second portion of the undopedsilicon oxide layer is performed before the etching and depositing theundoped silicon oxide film is performed after the etching.
 12. Themethod recited in claim 10 wherein depositing the second portion of theundoped silicon oxide layer comprises: flowing a second process gascomprising SiF₄, the fluent gas, the silicon source, and the oxidizinggas reactant into the process chamber; and forming a second plasmahaving an ion density of at least 10¹¹ ions/cm³ from the second processgas.